在sql中计算非零值

Question

我试图计算每个列大于零的总次数,按驱动程序名称分组.现在我有;

SELECT drivername
      , COUNT(over_rpm)      AS RPMViolations
      , COUNT(over_spd)      AS SpdViolations
      , COUNT(brake_events)  AS BrakeEvents
  FROM performxbydriverdata
 WHERE  over_rpm > 0
    OR over_spd > 0
    OR brake_events > 0
GROUP BY drivername

这给了我所有的非零值,但我得到一个显示为:

• 鲍勃史密斯62 62 62
• 内森琼斯65 65 65
• 等等

我试图在每个单独的值中计算非零值.每个违规都应该单独分组.

Answer 1

使用NULLIF将零更改为NULL,count忽略NULL

SELECT drivername,
     COUNT(NULLIF(over_rpm,0)) AS RPMViolations,
     COUNT(NULLIF(over_spd,0)) AS SpdViolations,
     COUNT(NULLIF(brake_events,0)) AS BrakeEvents
FROM performxbydriverdata
GROUP BY drivername;

您可以使用此组删除WHERE子句以提高性能,
或者由于匹配良好的索引而经常运行不良的条件

使用HAVING(根据其他答案)将删除所有3个聚合为零的行,这些行可能对您有用,也可能对您没用.如果需要,您可以添加此项.说,WHERE意味着至少有一行具有非零值,因此您不需要 WHERE和HAVING子句

Answer 2

将过滤谓词[s]放在带有case语句的Sum()函数内是一个有用的技巧,只要你需要根据某个谓词条件计算项目.

Select DriverName,
    Sum(case When over_rpm > 0 Then 1 Else 0 End) OverRpm,
    Sum(case When over_spd > 0 Then 1 Else 0 End) OverSpeed,
    Sum(case When brake_events > 0 Then 1 Else 0 End) BrakeEvents,
    etc.
FROM performxbydriverdata
Group By DriverName